Process for refining petroleum products



July 16, 1963 E. WEISANG ETAL 3,098,033

PROCESS FOR REFINING PETROLEUM PRODUCTS Filed Sept. 25, 1959 5 Sheets-Sheet 1 LsuLFu/e FREE FINAL SWEETENING' 8 REDUCING CATALYST 7 WS-E D/SULFIDES' REDUCED CATALY5T .fiPART/AL.

SWEETENING' /'-RE6ENE2ATo2 d. 2 5 T 0 \J "DIS'ULF/DES SOUR 2 OX/D/ZED INLET CATALYST MERCAPTIDES REDUCED CATALYST EDOUARD WEISANG CLAUDE SCHERRER ANDRE GISLON d wzfig Man/v35 Wad, A T TORN E YS July 16, 1963 E. WEISANG ETAL PROCESS FOR REFINING PETROLEUM PRODUCTS Filed Sept. 25, 1959 3 Sheets-Sheet 2 July 16, 1963 E. WEISANG ETAL PROCESS FOR REFINING PETROLEUM PRODUCTS Filed Sept. 25, 1959 3 Sheets-Sheet 3 United States Patent "cc 3,098,033 PRDCESS FOR REFENING PETROLEUM PRODUCTS Edouard Weisaug and tliaude Scherrer, Le Havre, and Andre Gislon, Paris, France, assignors to Socit Anonyme ditc: Compagnie Francaise dc Rafiinage, Paris, France, a corporation of France Filed Sept. 25, 1959, Ser. No. 842,346 Claims priority, application France Feb. 13, 1959 Ciaims. (Cl. zes-zzv This invention relates to the sweetening of petroleum hydrocarbons for the removal therefrom of such substances as mercaptans and the like and, more particularly, to a multi-stage continuous process for the removal from petroleum hydrocarbons of such mercaptan products by extraction elimination thereof with an alkaline material including an oxygenation catalyst which is continuously regenerated in the course of the process.

As is well understood, petroleum products often contain, inherently as a result of the origins thereof, various more or less important quantities or proportions of mercaptans and like sulphur-containing contaminants which, in addition to frequently producing an undesirable odor, may have other disadvantageous characterizing properties unless removed from the refined hydrocarbons. It has been suggested, of course, to alleviate this situation by oxidizing such mercaptan or other impurities to innocuous compounds such as disulfides, but, if it is attempted to carry out such an expedient, difficulties may be encountered by the fact that the disulfides are left in the refined product, and this may be particularly important in the case of gasoline and similar products where the presence of such disulfides may have an inhibiting effect on the action of certain common additives such as tetraethyl lead, etc.

To remedy the foregoing difficulties, it has also been suggested to eliminate mercaptans in petroleum products by extraction, rather than by oxidation in situ. For example, the petroleum products may be washed with a solution of alkali metal hydroxides containing such substances as cresols, alcohols, etc., which have the effect of augmenting the solubility of mercaptans in the washing or extracting liquid. After extracting mercaptans from the petroleum products, the alkaline solution is submitted to a regeneration operation either by steam stripping or by oxidation of the mercaptans to disulfides, the latter being then separated by settling the regenerated alkaline solutions. Such an oxidation step for regenerating the alkaline wash liquor is generally efiected by air in the presence of organic oxidation catalysts and at temperatures which, although only moderately elevated, are substantially above room temperature.

In such oxidation step, some difiiculties may be experienced with some of the oxidation catalysts utilized in actual practice. For example, diificulty may be experienced with solutions containing such catalysts, inasmuch as the solutions containing said catalysts are sensitive to oxidation and must therefore be protected against a too extended effect of oxygen. This is obtained by partial oxidation only of the mercaptid-es presentso as to leave a certain reducing potential of the solution due to a remainder of residual mercaptides. In such an event, there results in a re-cycling of mercaptanswith the washing alkaline extracting liquor and a reintroduction of mercaptans into the refined petroleum products, so that although the original mercaptan proportion of the petroleum products is diminished, they do not turn out to be doctor sweet.

According to the present invention, however, there is provided a process whereby, in a single, multi-stage op-. eration, the major part of the mercaptan impurities are removed from the petroleum products in a first extraction BfihdflB-E Patented July 16, 1963 step, then the extracting alkaline liquor is regenerated at room temperature, and then a second treating step is elfected with the regenerated alkaline liquor to eliminate from the petroleum product being refined remaining traces of mercaptans by way of oxidation so as to obtain a refined product which is doctor sweet; and oxidation catalysts are employed which are soluble or finely dispersible in the alkaline Washing solutions in adequate concentration for the extraction of the mercaptans in the form of mercaptides from the petroleum products, which oxidation catalyst must be sufiiciently stable chemically in presence of the caustic solution and also be characterized by being reversibly transformable from an oxidized form to a reduced form.

The foregoing and other objects and advantages of this invention will be apparent from the following description in the appended claims, and the accompanying drawings.

In the drawings- FIG. 1 is a diagrammatic or schematic flow-sheet illustration of the sequence of steps and operations embodying and for practicing this invention; and

FIGS. 2. and 3 are diagrammatic or schematic representations of the sequence of steps and apparatus embodying and for practicing this invention as particularly applied to two forms of processes for the treatment of gasoline.

Referring to FIG. 1, the general steps and stages of the multi-phase process according to this invention are indicated, along with the apparatus utilized therein. Thus, a counter-current extraction tower of conventional and well-known design is indicated at 1 into which the liquid petroleum product to be sweetened is introduced at an inlet indicated at 2 near the bottom of the column 1, while an alkaline washing and extracting solution containing the oxidation catalyst in the reduced form thereof is introduced to the upper portion of column 1 at 3 for counter-current extracting contact with the petroleum product introduced at 2. Since it is preferred to operate this invention in a continuous manner, counter-current flow through tower 1, as well understood, facilitates the continuous extracting contact of the alkaline washing and extracting liquid flowing down the tower with the petroleum product to be sweetened flowing up column 1. The alkaline washing and extracting liquid, having passed through column 1, is withdrawn therefrom at the bottom thereof through outlet 4, containing mercaptides and catalyst in the reduced form thereof. Such solution, withdrawn from column 1 through the outlet 4 thereof, is then subjected to a regenerating step in a conventional reactor or regenerator indicated at 5 during which step oxygen or an oxygen-containing gas is introduced into regenerator 5 at gas inlet 5a and bubbled through the alkaline liquor. As oxygen is bubbled through the liquor, the oxidation catalyst therein promotes the oxidation of mercaptides to disulfides at room temperature, and the thus-treated liquid is withdrawn from the regenerator 5 through the outlet line 6. Such liquid, after the oxidation step in regenerator 5, is substantially free of mercaptans (which have been oxidized to disulfides) and contains the oxidation catalyst in oxidized form. This product from regenerator 5 is then passed through a separation step indicated at 7 where the disulfides are separated from the alkaline liquor as by decantation or by extraction with a solvent which is immiscible in the alkaline liquor but capable of dissolving therefrom the disulfides.

The finally regenerated extraction or washing liquor emerging at 8 from the separation step or apparatus 7 is substantially free of sulfur compounds in any form and includes the oxidation catalyst now in its oxidized form, and this regenerated solution is passed to the upper portion of a further counter-current extraction column 10, while the partially sweetened petroleum product emerging from the top of column 1 at 9 is introduced into the lower portion of column 10 for a final sweetening step, conducted in the absence of air, and under the conjugated action of the regenerated alkaline solution and the oxidizing action of the oxidized form of the catalyst therein. The reaction in column 10 results in the substantially complete conversion to disulfides of any residual mercaptans which are not removed in the first extraction step in column 1, and also results in transforming the catalyst from the oxidized state to the reduced state thereof so that there is withdrawn from the outlet 11 at the bottom of column 10 an alkaline extraction solution containing catalyst in the reduced state for introduction at 3 to the first extraction step in column 1, while the petroleum product is withdrawn from column 10 at the top thereof through outlet 12 in a condition which is substantially free of mercaptans and doctor sweet.

The oxidation catalysts which are susceptible to utilization in an embodiment or according to this invention include, for example, the organo-rnetallic compounds with a chelate bond which are susceptible to or recognized as having the characteristic ability to absorb oxygen and desorb oxygen for providing an oxidized form, in one case, and a reduced form in the other case. Examples include such natural substances as haemoglobin or chlorophyll, or such synthetic products as ferrous indigo or salicylal-ethylene-diimino-cobalt, all as suggested in French Patent No. 996,851, and other products with neighboring structures such as the chelates derived from salicylal-alkylene-diirnine products as disclosed in French Patent No. 1,077,162, which products have the faculty of oxidizing mercaptans and, apparently, the property of oxidizing-reducing mentioned above although the oxidized form may not have been isolated. Such oxidation catalysts can also be, in addition to the chelates above mentioned, the sulfur dyes with regard to which the catalytic action according to this invention is suggested in French Patent No. 1,105,484, and, among the sulfur dyes particularly adapted to this process are those of the class 1002 of the Color Index disclosed in US. copending application Serial No. 800,454.

The aforementioned alkaline solution, one might mention here, is an aqueous solution of an alkali metal hydroxide, so concocted that the proportion of sodium hydroxide or potassium hydroxide is present in a concentration which comprises within the range of 5% to 45% of the entire alkaline solution, and this solution also should preferably, contain certain solvents for the mercaptans which it is desired to remove from the petroleum hydrocarbons being treated, such as, among others, cresols, alcohols, etc., although, as will be understood, this invention embodies the treatment of fractions of petroleum products with alkaline solutions which do not include such additional substances.

One of the principal objects of this invention is the regeneration of the alkaline solutions which are used to remove from the petroleum products the various impurities in accordance with this invention. In this connection, the regeneration of the aforementioned alkaline solutions, after an extraction of mercaptans, is accomplished by the complete oxidation of mercaptans in said alkaline solutions. One should note, however, that oxidation catalysts (or, at least, those designated below) have an activity such that they permit or enhance the oxidation of mercaptides at room temperature or at temperatures in that range, although perhaps a little above room temperature, nevertheless less than elevated temperatures, as for example, 15 to 50 C.

With such oxidation catalysts, as will be understood, a number of advantages according to this invention are achieved. A number of situations in which satisfactory results have been obtained according to this invention are noted hereinafter, as exemplary of the steps and processes embodying and for practicing this invention, and with which the regeneration of the alkaline solutions or extracts of the mercaptans which it is desired to remove from petroleum hydrocarbons are completed according to the foregoing. It should be noted, however, that the catalysts utilized in this extraction are particularly designated as those (whether chelates or sulfur dyes) as have a propensity for the oxidation (or which permit the oxidation) of mercaptides at room temperature (or at temperatures which are but little above room temperatures) as disclosed.

One may note from the foregoing, the following examples of catalysts and other considerations with which satisfactory results are achieved according to and embodying this invention.

As one example, one might note, the refining of a fraction of gasoline between initial and final points of 40 C. to C. and containing 140 g./m. of sulfur in the form of mercaptan. Utilizing, for the purpose of sweetening this particular gasoline fraction an alkaline solution containing 402 g./litre of caustic potassium hydroxide, g. of cresol and 1 g. of sulfur dye (Dark Green Sulfanol B, technical grade), the apparatus of FIG. 2 was used.

The dry and unconverted gasoline was provided at 13 at the rate of 60 m hr. and was mixed, at 14, with a conventional soda prewashing solution, to eliminate from the gasoline introduced into the system at 13 hydrogen sulfide in a manner which is well recognized. The particular treated gasoline was separated from the treating solution in a decanter 15, of well-known construction, and the soda solution was reclaimed by the pump 16 and re-cycled, as one would imagine for additional use, with, if necessary, a replenishment of soda solution from 16a, back through the decantation step of the decanter 15.

In the absence of oxygen, which is particularly remarkable in this invention, the gasoline was submitted to a number of extracting stages, two of which are illustrated in FIG. 2, for the appropriate extraction thereof, of the mercaptans; thus, the action of soda or potassium solutions, preferably containing cresols and containing Dark Green Sulfanol B or other sulfur dyes in a reduced state, is achieved, as indicated in the reactors 1717a (with particular regard to FIG. 2), in the proportion of 6 volumes of gasoline (or other petroleum products) to 1 volume of alkaline solution containing the cresols, etc., as aforementioned.

From decanter 17a there exits a petroleum product containing, still, something of the order of 60 g./rn. of mercaptans, which product, as will be understood, cannot be considered as sweetened.

Out of the decanter or reactor 17 is produced an extraction solution, in the alkaline and aqueous phase, enriched in mercaptans, which solution is conducted by the piping designated at 18 into the regenerating reactor 19 Where the aqueous phase solution is submitted to the action of air, interjected into reactor 20 at a temperature of about 20 C. Because of the presence of a sulfur dye (such as Dark Green Sulfanol B) acting as the catalyst, the mercaptides are oxidized into disulfides in the presence of the sulfur dye, which is converted to its higher oxidized state. Any excess of air is withdrawn through 21, and the alkaline solution therein, freed of mercaptans but containing disulfides, is thereafter directed by the outlet line 22, to the system of mixer-settler 23-44 and subjected to extraction by means of a solvent. The solvent charged with disulfides, is eliminated in line 25, and the fresh solvent is introduced, as by line 26, and the alkaline regenerated solution containing the catalyst in oxidized state is withdrawn by the line 27. The gasoline, still containing a minor amount of residual mercaptan, which leaves the decanter 17, and the regenerated extraction solution arriving by line 27, are flowing together to the mixer-reactor 28, to be treated in the absence of air, as above noted. The Dark Green Sulfanol B is reduced, in

this step of the reaction, by the residual mercaptans in the gasoline, and there is withdrawn at 29 a gasoline fraction which is sweet, and there is withdrawn at 30 an aqueous extraction phase containing the reduced catalyst so that this alkaline solution after being renewed by contact with the gasoline to be refined, is capable of extracting mercaptans, without oxidation thereof and therefore without introduction of corresponding disulfides into the gasoline to be refined.

In order to compensate for the losses of catalysts in the foregoing system, a replenishment of catalysts (for example, Dark Green Sulfanol B) is effected as, for examplc, through the piping 31, as may be necessary.

As indicative of the enhanced results of a system embodying and for practicing this invention and as indicated, schematically and diagrammatically in FIG. 2, one may note the satisfactory or indicative data of Table I with regard to such a system. For example, Table I indicates the extent of retained mercapt-an and disulfide in two trials which were made, the one trial without a catalyst which embodies this invention and the other with an oxidation catalyst as described in accordance with this invention, which trial proved, indeed, the advantage of the present invention and the practice thereof in which one is concerned with the obtaining of :a truly sweet refined fraction and the regeneration, at room temperature, of a useable alkaline extracting solution.

Table I Trial Trial Without With Catalyst Catalyst Gasoline to be treated:

Initial boiling point C.) 40 40 Final boiling point C.) 160 160 Proportion of sulfur retained as mereaptan g/m. 140 140 Operating Conditions:

Throughput of gasoline (mfi/hr.) 60 60 Throughput of alkaline solution (m. /h1'.) 11.2 Extraction temperature C.) 20 Extraction:

Sulfur as mercaptan (g./m. 50 60 Retained disulfides (gJmfi) 0 0 Final extent of refining:

Residual content of sulfur as mercaptans (g./m. 60 0 (sweet) Regeneration of alkaline solution:

Content of sulfur as mercaptans at the entrance of the regenerator (g./l00 cmfi) 0.090 0.050 Content of sulfur as mereaptans upon the exit from regenerator (g./l00 emfi) 0.051 0 Temperature of regeneration C.) 60 20 Duration of regeneration (minutes) 40 40 As a second example, a gasoline fraction was treated continuously in apparatus of the character described in which the gasoline throughput was of the order of substantially 50 m. per hour, with the gasoline fraction being generally, characterized as having an initial boiling point of 40 C. and a final boiling point of 160 C. and containing prior to extraction, 160 g./m. sulfur :as mercaptans. This gasoline fraction was treated by extracting with an alkaline solution containing 350 g./lit-re of potassium hydroxide at the rate of 15 m. /hr., which alkaline solution also contained 1 g. litre sulfur dye and :a feeble quantity (of approximately g.) of phenol, merely to obtain a suflicient dispersion of the dye in the alkaline solution.

At various different stages of this treatment, the following data was obtained.

Table [I At the exit extractor Gasoline Percent sulfur (as mercaptan) 80 g./m. Percent sulfur (as disulfides) Traces, Alkaline solutionPercent sulfur (as Traces.

As another illustration of a situation embodying and for practicing this invention and involving another situation or embodiment of apparatus as, for example, is illustrated in FIG. 3, 60 mfi/hr. of a reformer gasoline cut was treated (which gasoline fraction was between the boiling points of 41 C. and, as a final boiling point, 192 C.) and contained approximately (after the washing thereof) something of the order of 330 g./m. sulfur in the form of mercaptans and a concomitant amount of sulfur (perhaps 19 g./rn. in the form of disultides. This type of gasoline fraction was treated with an alkaline solution of potassium hydroxide with, as will be understood, approximately g./litre cresol and approximately 3 g./litre chelates of cobalt, in the mentioned alkaline solution at the rate of, approximately, 12 1n. /hr. with this treatment. The untreated gasoline was treated by such a system and interjected into the apparatus of FIG. 3 as, for example, at the line 32 and was mixed in the mixer 33 where it is discharged with a 10% soda solution, which mixture is, as will be understood, separated in known manner in the decanter 34 and, since the soda or alkaline washing solution is recycled by pump 35, the pre-washed gasoline fraction is led, through the piping 36 and into the extractor 37 (which apparatus is of a well-known nature and, preferably, includes an agitator for the purpose of agitating or otherwise intermixing materials led thereinto). The reactor 37 is, as will be understood, a counter-current type in which the alkaline extracting solution has a great opportunity to contact the petroleum products to be refined, and the alkaline solution according to this inven tion, for the purpose of extraction, is introduced, with the oxygenation catalyst in a reduced state, for the preliminary extraction, through the pipes 36 into the reactor. From the reactor and through the piping 38, the alkaline solution (including, of course, the oxygenation catalyst, still in a reduced state) is submitted (as, for example, in the reactor 39) to contact with air or a gas containing oxygen interjected into the regenerator 39, at, as for example, the gas inlet 40, and preferably, at a temperature approximately room temperature and/or 20 C. In this operation mercaptides, contained in this alkaline solution, are oxidized to disulfides and the oxygenation catalyst (whether chelate or sulfur dye) is transformed to an oxidized form as compared to a reduced form.

In this step of the operation, as will be understood, the mercaptans or mercaptides are oxidized and the reduced chelates catalyst is transformed to its respective oxidized forms. So, from the regenerator there is withdrawn an alkaline liquid or liquor which can be subsequently submitted through line 42 to the extraction of the disulfides, whcih alkaline liquor is excessively purged by air or other oxygen-containing gas at 41. Thus, there is accomplished a two-stage operation with the static reactors 4-3-44 in their own operation, along with the decanters 45-46. Thus, the disuifides of this operation are extracted, through the piping 48 and as treated in reactors 49, with the gasoline exiting at 50 from the extractor 49 completely free of any charge of residual mercaptans. In this reactor, the residual mercaptans (which may have, possibly, remained with the gasoline fraction through the first extraction stage) are oxidized to disulfides by the chelate catalyst as may be required, and such oxidation also, in effect, transforms the chelate catalysts to a reduced (or de-oxygenated) form thereof so that they are once again, in the mixture of the alkaline washing or extracting liquor, able to perform the function (with or without cresol, etc.), of an extractant at the entrance 37 thereof or by the piping 51, as may be desired for the regeneration of the particular catalyst for accomplishing the refining of the gasoline withdrawn from the apparatus at 52.

As further indicative of the accomplishments made by the various effects and/ or embodiments of this invention, the following may be noted as a matter of illustrative results.

Thus, as indicative of the enhanced advantages of this invention, one may note the data of a gasoline fraction processed according to the teachings and/or disclosure of FIG. 3, as, for example, relating to:

Table 111 Volume of gasoline treated 6O mF/hr, Volume of extracting solution circu1ated 12 mi /hr. Gasoline (pro-washed) Percent sulfur (as mercaptan) 330 g./m. Percent sulfur (as disulfide) 19 g./1n. Upon exit from extractor Percent sulfur in treated gaso1ine As mercaptans 37 g./m. As disulfides 22 g./rn. Percent sulfur in alkaline extracting solution (as mercaptans) 1.420 g./111. Upon exit from the regenerator:

Alkaline solution sulfur percent (as mercaptans) Traces. Upon exit from reactor Sulfur in gasoline fraction (as mercaptans) Traces (indefinable). Percent sulfur (as disulfides) 6O g./m.

While this invention has been described and exemplifled in terms of its preferred embodiments, those skilled in the art will appreciate that modifications may be made without departing from the scope of the invention as defined in the appended claims.

We claim: 1

1. In a process for refining petroleum hydrocarbons by the removal therefrom of sulfur impurities present therein as mercaptans, the steps which comprise extracting from said petroleum hydrocarbons a major portion less than all said mercaptans with an aqueous alkaline solution including an organic oxidation catalyst undergoing reversible transformation between an oxidized state and a reduced state, said catalyst being in said reduced state during said extracting step and said extracting step being conducted in counter-current flow in a closed system and substantially in the absence of oxygen, separating from said extracting step a hydrocarbon phase containing a minor portion of said original merca-ptans and an aqueous alkaline phase containing said extracted major portion of mercaptans as mercaptides, subjecting substantially all of said separated aqueous alkaline phase to an oxidizing step for oxidizing said mercaptans in said aqueous alkaline phase to disulfides and effecting during said oxidizing step conversion of said catalyst in said aqueous phase from said reduced state to said oxidized state thereof, separating said disulfide produced in said oxidizing step from said aqueous alkaline phase for obtaining a regenerated aqueous alkaline solution containing said catalyst in said oxidized state thereof, treating said hydrocarbons from said first extracting step with said regenerated aqueous alkaline solution in a second treating step for oxidizing said minor portion of said mercaptans therein and effecting conversion of said catalyst back to said reduced state thereof, said second treating step also being conducted with countercurrent flow and in a closed system substantially in the absence of the addition of oxygen thereto, withdrawing from said second treating and oxidizing step said petroleum hydrocarbons substantially free of mercaptan impurities, separately withdrawing from said second treating and oxidizing ste said alkaline solution containing said catalyst converted to said reduced state thereof, and recycling substantially all of said withdrawn alkaline solution directly into said first extracting step through a closed system and substantially in the absence of the addition of oxygen thereto for extracting said mercaptans from additional said petroleum hydrocarbons in said first extracting step.

2. A method in accordance with claim 1 in which said alkaline solution comprises an aqueous solution of an alkali metal hydroxide.

3. A method in accordance with claim 2 in which said alkaline solution comprises a solution of potassium hydroxide.

4. A method in accordance with claim 1 in which said alkaline solution also includes an organic substance containing a hydroxyl group for enhancing the solubility of mercaptides in said aqueous alkaline phase.

5. A method in accordance with claim 1 in which said catalyst is a metallic chelate.

6. A method in accordance with claim 5 in which said catalyst is a cobalt chelate from a Schiff base resulting from the condensation of a hydroxybenzaldehyde and diamine.

7. A method in accordance with claim 1 in which said catalyst is a sulfur dye.

8. A method in accordance with claim 7 in which said sulfur dye is No. 1002 of the Color Index.

9. A method in accordance with claim 1 in which said oxidizing and regenerating step of said alkaline solution is conducted substantially at room temperature.

10. A method in accordance with claim 1 in which said oxidizing and regenerating step of said alkaline solution is conducted by bubbling through said solution an oxygen-containing gas.

References Cited in the file of this patent UNITED STATES PATENTS Gislon et al July 28, 1959 Urban et al Jan. 12, 1960 OTHER REFERENCES 

1. IN A PROCESS FOR REFINING PETROLEUM HYDROCARBONS BY THE REMOVAL THEREFROM OF SULFUR IMPURITIES PRESENT THEREIN AS MERCAPTANS, THE STEPS WHICH COMPRISE EXTRACTING FROM SAID PETROLEUM HYDROCARBONS A MAJOR PORTION LESS THAN ALL SAID MERCAPTANS WITH AN AQUEOUS ALKALINE SOLUTION INCLUDING AN ORGANIC OXIDATION CATALYST UNDERGOING REVERSIBLE TRANSFORMATION BETWEEN AN OXIDIZED STATE AND A REDUCED STATE, SAID CATALYST BEING IN SAID REDUCED STATE DURING SAID EXTRACTING STEP AND SAID EXTRACTING STEP BEING CONTACTED IN COUNTER-CURRENT FLOW IN A CLOSED SYSTEM AND SUBSTANTIALLY IN THE ABSENCE OF OXYGENM SEPARATING FROM SAID EXTRACTING STEP A HYDROCARBON PHASE CONTAINING A MINOR PORTION OF SAID ORIGINAL MERCAPTANS AND AN AQUEOUS ALKALINE PHASE CONTAINING SAID EXTRACTED MAJOR PORTION OF MERCAPTANS AS MERCAPTIDES, SUBJECTING SUBSTANTIALLY ALL OF SAID SEPARATED AQUEOUS ALKALINE PHASE TO AN OXIDIZING STEP FOR OXIDIZING SAID MERCAPTANS IN SAID AQUEOUS ALKALINE PHASE TO DISULFIDES AND EFFECTING DURING SAID OXIDIZING STEP CONVERSION OF SAID CATALYST IN SAID AQUEOUS PHASE FROM SAID REDUCED STATE TO SAID OXIDIZED STATE THEREOF, SEPARATING SAID DISULFIDE PRODUCED IN SAID OXIDIZING STEP FROM SAID AQUEOUS ALKALINE PHASE FOR OBTAINING A REGENERATED AQUEOUS ALKALINE SOLUTION CONTAINING SAID CATALYST IN SAID OXIDIZED STATE THEREOF, TREATING SAID HYDROCARBONS FROM SAID FIRST EXTRACTING STEP WITH SAID REGENERATED AQUEOUS ALKALINE SOLUTION IN A SECOND TREATING STEP FOR OXIDIZING SAID MINOR PORTION OF SAID MERCAPTANS THEREIN AND EFFECTING CONVERSION OF SAID CATALYST BACK TO SAID REDUCED STATE THEREOF, SAID SECOND TREATING STEP ALSO BEING CONDUCTED WITH COUNTER-CURRENT FLOW AND IN A CLOSED SYSTEM SUBSTANTIALLY IN THE ABSENCE OF THE ADDITION OF OXYGEN THERETO, WITHDRAWING FROM SAID SECOND TREATING AND OXIDIZING STEP SAID PETROLEUM HYDROCARBONS SUBSTANTIALY FREE OF MERCAPTANS IMPURITIES, SEPARATELY WITHDRAWING FROM SAID SECOND TREATING AND OXIDIZING STEP SAID ALKALINE SOLUTION CONTAINING SAID CATALYST CONVERTED TO SAID REDUCED STATE THEREOF, AND RECYCLING SUBSTANTIALLY ALL OF SAID WITHDRAWN ALKALINE SOLUTION DIRECTLY INTO SAID FIRST EXTRACTING STEP THROUGH A CLOSED SYSTEM AND SUBSTANTIALLY IN THE ABSENCE OF THE ADDITION OF OXYGEN THERETO FOR EXTRACTING SAID MERCAPTANS FROM ADDITIONAL SAID PETROLEUM HYDROCARBONS IN SAID FIRST EXTRACTING STEP. 